Formula

Hi, so my son is 6.5 weeks and I’ve tried to exclusively pump for him (with the breast, he was always hungry and fussy) so this way I see how much he’s getting and he’s eating every 3-4 hours during the day. However, I had a difficult time keeping up with him bc he’s a big boy (12lbs) so I’ve started to supplement. I’m noticing he spits up LESS with the formula than the breast milk. What does this mean? Does he tolerate the formula better than me? I don’t drink or smoke or eat spicy food. What should I do if anything? Thank you.